Treatment of dry cleaning baths

ABSTRACT

HYDROGEN PEROXIDE IS USED IN THE TREATMENT OF DIRTY DRY CLEANING BATHS BASED ON ALIPHATIC HYDROCARBON OR CHLORINATED SOLVENTS, TO PERMIT LONGER OPERATION BETWEEN DISTILLATIONS.

3,677,955 TREATMENT OF DRY CLEANING BATHS I Int. Cl. 011a 7/50 us. or. 252-162 2 Claims ABSTRACT OF THE DISCLOSURE Hydrogen peroxide is used in the treatment of dirty dry cleaning baths based on aliphatic hydrocarbon or chlorinated solvents, to permit longer operation between distillations.

BACKGROUND OF THE INVENTION In the dry cleaning of garments and other articles made of textile fabrics, the general technique involves exposing the garments, etc., to the action of a bath consisting of a solvent such as mineral spirits, trichloroethylene, perchloroethylene or trifiuorotrichloroethane, containing from about 0.5 to 5.0% of a detergent, and a very small amountfrom about 0.02 to 0.12%-of water, using from about 5 to 20 times as much bath as weight of fabric. The bath is circulated through the garments for a short period of time, typically 5 to 20 minutes at room temperature, picking up in the process particles of dirt which become suspended in the bath, dissolving such materials as greases and oils, which are soluble in the solvent, and emulsifying any water which may be present in the garments. After separation from the garments, the liquid may be reused as it, or treated with a dehydrating agent to reduce its water content, or filtered to remove the solid matter removed from the garments. Eventually, the solvent must be distilled to clean it up. The distillation is the most expensive way to clean up the solvent, since it entails both operational costs and loss of the expensive detergent, which must be replaced. Hence, it is desirable to reduce the frequency of distillation.

STATEMENT OF THE INVENTION We have found that, surprisingly, treatment of dirty dry cleaning baths with aqueous hydrogen peroxide by simple agitation at room temperature for short periods of time, with at least enough aqueous hydrogen peroxide to just more than saturate the bath, followed by distillation, results in sufficient cleaning of the dirty baths so that distillation can be postponed for a sufficient time to permit substantial cost savings.

DETAILED DESCRIPTION OF THE INVENTION as the isopropylamine salt of dodecylbenzene sulfonatewill have a high transmission of light, ranging from 91% States Patent .Office 3,677,955 Patented July 18, 197 2 for light at 450 mu to 94.2% at 500 my, to 99.1% at 600 m When the transmission at 500 m drops to the vicinity of 50% (after the filtration which itgenerally undergoes after each cleaning cycle), the cleaning bath is generally considered too dirty for further cleaning and is distilled. This costs. about twenty-five cents per pounds of solvent, plus the cost of the detergent which must be added to reconstitute the cleaning bath.

We have found that if dirty dry cleaning baths heretofore considered unfit for use without distillation are treated with aqueous hydrogen peroxide, suflicient cleanup can be obtained to permit the reuse of the bath without distillation, if the bath is treated with more hydrogen peroxide than the bath will hold in the systemi.e., more than a few tenths of a percent of combined peroxide and water. If insuflicient hydrogen peroxide is present to more than saturate the bath, substantially lower cleaning efficiency is obtained than when the same amount of hydrogen peroxide is used together with enough water to more than saturate the system.

We believe there is a dual action taking place. There is bleaching action by the peroxide which decreases the light absorption. But a major proportion of the clean-up appears to be due to some physical eifect on the suspended dirt by the fine particles of excess aqueous peroxide suspended in the system, which we believe act as nuclei for the agglomeration of small dirt particules to a size where they will filter out. This view is reinforced by experimental evidence. For example, a dirty perchloroethylene bath whose transmittance had fallen to 53% of 500 mu was treated with 0.5% of 50% aqueous hydrogen peroxide for 30 minutes at 25 C. The mixture was filtered through diatomaceous earth in conventional fashion, and had a transmittance of 66%. The same solvent, treated with the same amount of water under the same conditions, had a transmittance of 60%. The same solvent, treated to remove water, and then treated with 0.255% of 98% hydrogen peroxide, also had a transmittance of about 60%, indicating that the action is only about half-bleaching.

The amount of aqueous hydrogen peroxide needed depends on the bath, since the water-carrying capacity varies with both solvent and detergent. However, the actual amount of peroxide used need not vary, since more or less water can be added with it. Since water alone in suflicient quantity produces an improvement, any amount of peroxide will contribute its bleaching power. Up to about 0.25% of hydrogen peroxide (100% basis), based on bath weight, there is a definite increase in transmission as peroxide increases; above about this figure, the additional transmission per unit falls off, and becomes uneconomic, at points which vary with the composition of the bath, and the nature of the dirt picked up in the cleaning process, and the concentration of the peroxide. Amounts of peroxide above about 0.5% are, in general, economically unattractive.

SPECIFIC EXAMPLES OF THE INVENTION Example l.--Perchloroethylene bath A dry cleaning bath containing perchloroethylene with 1% of the isopropylamine salt of dodecylbenzene sulfonate was prepared; its light transmittance was 450 m,u- 91%; 500 m;t94.2%; 600 m,u-99.l%. It was used in cleaning until its transmission at 500 mu dropped to 50%, and was treated with 0.25% of hydrogen peroxide, in one case as 98% H 0 in the others as 50% H 0 by stirring the peroxide into the dirty bath and filtering throughdiatomaceous earth; the following transmissions were measured on the sample:

Transmission at 0.255 weight percent H102 (98%) 43 59. 7 72. 3 0.5 weight percent H20; (50%) 46 66.0 81.0

The physical effect of more water plus peroxide than the system will hold is clearly demonstrated.

Example 2.-Stoddard solvent We claim:

1. The method of treating dirty dry cleaning baths consisting of a volatile oil solvent and a detergent to permit longer operation between distillations, which comprises agitating the dirty bath with at least 0.25% aqueous hydrogen peroxide, and filtering the bath to remove suspended dirt and fine particles of excess aqueous hydrogen peroxide to obtain a cleaned bath.

2. The method of claim 1, in which the hydrogen peroxide is not in excess of 0.50% of bath weight.

References Cited UNITED, STATES PATENTS 3,203,754 8/1965 Young et al 8142 2,371,545 3/1945 Riggs et al. 252.95 2,886,532 5/1959 Richmond et a1. 252-104 3,452,110 6/1969 Cooley et a1. 8142 1,395,694 11/1921 Allinson 208--179 HERBERT B. GUYNN, Primary Examiner W. E. SCHULZ, Assistant Examiner US. 01. X:R. s 141, 142 

